1. Field of the Invention
The present invention relates to a micromirror actuator, and more particularly, to a micromirror actuator which is capable of precisely adjusting the inclination angle of a mirror.
2. Description of the Related Art
Micromirror actuators are optical switching devices used in optical transmission devices and holographic optical data recorders. In holographic optical data recorders, mirrors are required to be placed at precise positions for correctly changing an optical path or switching. A plurality of micromirror actuators are installed in an array in a holographic optical data recorder and must show the same mirror operational characteristics.
FIG. 1 illustrates a conventional micromirror actuator, in which two posts 2a and 2b are installed a predetermined distance apart on a substrate 1, and torsion bars 3a and 3b are formed to extend from a mirror 3. The torsion bars 3a and 3b are respectively connected to two posts 2a and 2b at one end. In addition, magnets 4a and 4b are placed at two opposite sides of the mirror 3.
Referring to FIG. 1, the mirror 3 inclines over the substrate 1 by a predetermined angle due to a vertical magnetic field emanating from the substrate 1. Here, one edge of the mirror 3 is in contact with the surface of the substrate 1, and thus the inclination angle of the mirror 3 with respect to the substrate 1 can be maintained. When the mirror inclines over the substrate 1, the torsion bars 3a and 3b having predetermined elastic forces are twisted.
FIG. 2 illustrates the conventional micromirror actuator of FIG. 1 in a state where there is no magnetic field. If the magnetic field affecting the micromirror actuator of FIG. 1 is removed, as illustrated in FIG. 2, the mirror 3 rotates about the torsion bars 3a and 3b so as to be parallel with the surface of the substrate 1 due to the elastic restoring forces of each of the torsion bars 3a and 3b. 
As shown in FIG. 1, when the mirror 3 is inclined over the substrate 1 by 45 degrees, light, which enters the micromirror actuator of FIG. 1 parallel to the surface of the substrate 1, is reflected perpendicular to the substrate 1 by the mirror 3. On the other hand, light, which enters the micromirror actuator of FIG. 2, directly passes over the surface of the mirror 3 without being reflected by the mirror 3. The operation of the micromirror actuator is controlled by the external magnetic field mentioned above. In most cases, an electromagnet is attached on the bottom surface of the substrate 1 in order to form such a vertical magnetic field.
As shown in FIG. 3, when an external magnetic field is formed, the mirror 3 can rotate about the torsion bars 3a and 3b against the elastic forces of the torsion bars 3a and 3b so as to form a predetermined angle with the substrate 1. On the other hand, when there is no external magnetic field, the mirror 3 rotates so as to be parallel with the surface of the substrate 1 due to the elastic restoring forces of the torsion bars 3a and 3b. 
However, as shown in FIG. 4, if a strong external magnetic field is applied to the microactuator after one edge of the mirror 3 has contacted the surface, the torsion bars 3a and 3b cannot maintain their straight shapes and are inevitably bent due to their flexibility. Here, the fact that the torsion bars 3a and 3b cannot maintain their straight shapes, means that the rotation axis of the mirror 3 changes and accordingly, the rotation angle of the mirror 3 exceeds a desired level. The torsion bars 3a and 3b are supported at one end by the posts 2a and 2b, respectively. Accordingly, it becomes difficult to obtain a normal inclination angle of the mirror 3 in the conventional actuator, in which the mirror 3 and the torsion bars 3a and 3b are connected to one another. Dotted lines 3axe2x80x2 and 3bxe2x80x2 in FIG. 4 indicate the original shapes of the torsion bars 3a and 3b, respectively, before the lower edge of the mirror 3 contacts the substrate 1 and the torsion bars are abnormally deformed. Solid lines in FIG. 4 indicate the shapes of the torsion bars 3a and 3b, respectively, abnormally deformed due to the rotation of the mirror 3.
As described above, if the mirror 3 is sufficiently rotated until one edge of the mirror 3 contacts the surface of the substrate 1 and thus the torsion bars 3a and 3b are deformed, the rotation center of the mirror changes, and the rotation angle of the mirror 3 exceeds a designed angle range. Accordingly, it is impossible to reflect light in a desired direction in an apparatus using the conventional micromirror actuator as an optical switching device.
To solve the above-described problems, it is an object of the present invention to provide a micromirror actuator which is capable of precisely adjusting the rotation angle of a mirror.
Accordingly, to achieve the above object, there is provided a micromirror actuator including a substrate, posts formed to a predetermined height on the substrate and spaced a predetermined distance apart, a torsion bar fixed to the posts, a mirror coupled to the torsion bar, and a groove including an inclined contact surface and formed in the substrate. Here, the inclined contact surface contacts the lower bottom surface of the mirror when the mirror is rotated.
Preferably, a driving electrode or a clamping electrode for generating electrostatic forces to clamp the mirror is formed on the inclined contact surface of the groove.
Preferably, the torsion bar is formed on the same plane as the mirror and the mirror is formed to rotate about the torsion bar.
Preferably, a plurality of magnets are arranged on an area of the mirror corresponding to the inclined contact surface.